Wind energy conversion devices

ABSTRACT

A wind turbine for harvesting energy from both horizontal and vertical wind currents having an open frame structure and a central passage through the structure with at least three wind energy harvesting generally vertically disposed and rotatably mounted blades positioned about the central passage and at least three wind energy harvesting generally horizontal blades projecting radially from the central vertical axis of the device. The open frame structure includes a unique rod and cable central structure offset from the periphery of the frame. In one embodiment, the frame structure is suspended from a rotatable hub at the top of a stationary mast.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation of copending U.S. patentapplication Ser. No. 14/028,035 filed Sep. 16, 2013 and to issue as U.S.Pat. No. 9,453,495 on Sep. 27, 2016, which is a continuation of U.S.patent application Ser. No. 13/601,378 filed Aug. 31, 2012 and issued asU.S. Pat. No. 8,534,987 on Sep. 17, 2013, which is a divisional of U.S.patent application Ser. No. 13/007,311 filed Jan. 14, 2011 and issued asU.S. Pat. No. 8,257,018 on Sep. 4, 2012, which claims the benefit ofU.S. Provisional Application No. 61/295,053 filed Jan. 14, 2010, thecontents of which are incorporated by reference herein.

FIELD OF THE INVENTION

This invention pertains to rotary devices that efficiently andeconomically convert the kinetic energy of wind into electricity in avariety of settings including in building-laden urban areas.

BACKGROUND

It is well known that we are at a point of “Peak Oil” where discovery ofnew sources of oil is less than the amounts being depleted. There isalso growing concern over pollution produced from burning fossil fuels,especially coal to generate electricity. Concurrently, demand forelectricity continues to grow across the globe. Consequently, increasingeffort is being devoted to developing devices that harness renewableenergy sources to generate electricity. Wind turbines are one of these.

Turbines that operate in windy environments have traditionally falleninto descriptive categories defined by their axis of revolution relativeto the wind and/or the ground. Vertical axis wind turbines (VAWTs) haveblades that are generally parallel to their axis of spin andperpendicular to the ground while horizontal axis wind turbines (HAWTs)have blades that are generally perpendicular to their axis of spin andparallel to the ground. The VAWT and HAWT nomenclature popularly relatesto the ground plane but is not dependent upon it.

In order to successfully generate usable energy, a wind turbine mustminimize mechanical energy losses while producing the maximum practicalextraction of torque from the wind. Wind turbines, though they need tobe strong, should be as light as possible in order to minimize energylosses due to inertia and mechanical friction. Also, since the velocityand direction of the wind varies continuously, there is a need forturbines that can harness a wide range of wind velocities and oftenvarying wind directions with the least internal mechanical energy loss.Because wind velocity varies greatly over the course of a year, it isimportant that wind turbines be able to harness both low and highvelocity winds. Since it is often difficult to initiate movement of suchdevices, there is a particular need for wind turbines that areself-starting at lower wind speeds, just as there is a need for designsthat produce structural and material efficiencies that handle thestresses experienced by wind turbines when operating at higher windspeeds.

Wind turbine devices, though producers of “green” energy, also mustovercome their own environmental challenges. Increasingly people areobjecting to the flickering shadows and noise generation of currentlyproduced and installed HAWT wind turbines when they are within sight andearshot of homes, businesses, places of recreation, etc. HAWT turbinesalso tend to create problems for birds and bats as they can be struck bythe wind turbine blades, or sustain internal organ damage due to the lowpressures generated near the moving blades. Therefore, there is a needfor new types of installed wind turbines that are aesthetically pleasingin appearance, fit more comfortably into their environment, and do notgenerate low pressures in the vicinity of their moving blades.

Finally, the art has not thus far provided efficient and practical largeand medium scale wind turbines that can be placed and effectively usedin congested and populated locations including in urban areas filledwith buildings, including skyscrapers. Further, the wind turbineindustry has not developed sufficiently efficient and otherwiseacceptable turbines that can be successfully erected and operated inurban areas or atop tall buildings including skyscrapers to generatesignificant kilowatt output. The industry also has not recognized thepotential of unique air flow accessible in such environments or how tobest harness them efficiently. Therefore, the increased wind poweravailable at the heights of tall buildings and the beneficial wind flowavailable across the tops of such buildings have not yet beenefficiently harvested.

Finally, the wind turbine industry is increasingly plagued more by theinfrastructure related costs of erecting ever taller turbines andgetting the electricity that they produce to market rather than by thecosts of the turbines themselves. These infrastructure utilization costsinclude the costs of erecting free-standing towers and the costs of newor upgraded electrical distribution grids that link the wind turbinesand the electricity they produce to where it is used. Distance also cancreate considerable transmission line losses which may be as high as20%. Such transmission line losses could be virtually eliminated byreducing transmission distance, if acceptably designed and efficientmid- to large-size turbines were available for placement in the urbanenvironment, particularly on the top of tall buildings. Green, renewablygenerated electricity is easily used within these turbine-toppedbuildings by tenants and building management. Placement atop tallbuildings would also eliminate the costs of erecting towers to supportand elevate wind turbines.

The various embodiments of the present invention overcome thesedifficulties and meet operational requirements and more with devicesthat (a) are extremely lightweight and subject to very low friction andinertial losses; (b) can accommodate a wide range of wind velocities andvarying wind direction; (c) allow feathering of the wind-receivingblades of the device to maximize power output and reduce drag in thereverse wind portions of the turbines' rotation; (d) maximize the torque(power) produced through just-in-time sensing of wind conditions at theblades which enhance feathering control and optimally maximize torqueextraction; (e) have a visually appropriate appearance and do notgenerate low pressures in the vicinity of their moving blades; (f) aregenerally quiet in operation; (g) start up without external assistancein low winds; (h) can harness both high and low velocity winds (andaddress occasionally very high winds without structural failure; (i) aredesigned to resist centrifugal forces on turbine components; (j) can beplaced atop tall buildings where the wind benefits of height and otherspecific conditions can be captured; (k) capture unique air flow frombuilding-induced updraft available at skyscrapers; and (l) may be usedto supply power directly via a minimal transmission distance to the verybuildings onto which they are erected thereby minimizing powertransmission losses of that electricity that is generated by theturbine.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

The embodiments of the present invention include wind turbines withgenerally vertically disposed blades evenly spaced about and parallel tothe vertical axis of the device which is generally perpendicular to theground. In preferred embodiments these wind turbines, also includeadditional blades that are generally radially disposed about the samevertical axis (generally parallel to the ground) and generallyperpendicular to that axis. Thus, all of the turbine blades drive aboutthe same axis though they have different orientations to it. Embodimentsof the invention can be located atop high-rise buildings or on freestanding towers, particularly free standing towers having solid facadeson their sides preferably extending the full height of the towers, or onother supporting structures. The power generated can be used to createelectricity for use on location or sold back to the electrical grid.

When both the vertically and horizontally disposed blades are present inembodiments of the invention, the device is able to capture previouslyuncaptured wind flow. This is particularly an advantage for urban usebut can also be implemented in other environments.

Wind in its natural state, when unobstructed, flows horizontally abovethe ground surface. As the elevation above the ground surface increases,the wind tends to flow at a greater speed. This is important because thepower that can be harvested from the wind increases to the third poweras wind speed increases. Natural horizontal wind produces upward airflow at a vertical obstructing surface. The urban condition withbuildings, landscape and trees tends to produce turbulence in the windnear the ground though less turbulence as the elevation increases. It isan important objective of this invention to provide a wind turbine thatcan be used efficiently in an elevated environment at least 50 feet andpreferably at skyscraper height where higher wind speeds that are onlymoderately turbulent are encountered and, in preferred embodiments, thatcan also capture and use the building-induced air flow.

The various embodiments of the invention can be “building” mounted or“tower mounted” with the axis of the turbine generally vertical to theground. They therefore have characteristics of a VAWT type device. Evenhigh above the ground some turbulence remains. VAWTs are known to beless affected by turbulent wind than HAWTs. VAWTs are also known to benaturally omnidirectional and by definition always face the wind incontrast to HAWTs which must always be turned to face directly into thewind. VAWTs are therefore efficient in this respect and excellent fornatural or environmental wind as no mechanical energy is used andtherefore wasted in tracking the wind direction, which in urbanenvironments is generally quite variable.

Any building (or façade-covered tower) is an obstruction to natural windand a tall building is a large obstruction to a large cross-section ofthe wind. The obstruction to the wind caused by a tall building (orfaçade covered tower) results in large static and dynamic forces appliedto the building. Tall buildings are designed to structurally resist thesubstantial stresses caused by obstruction of the most extreme windsexpected with a significant factor of safety. The turbine is intended tooperate in moderate and strong winds, but will occasionally be ‘parked’in the most extreme winds which generate the highest loads on thebuilding. In its parked position the blades will be oriented to minimizethe forces on the turbine and those transmitted to the supportingbuilding or tower. In this state the wind forces on the turbine will besmall compared to those on the building as a whole, and in view of thenormal conservatism and safety factors adopted in building design mostexisting tall buildings will be able to support turbines of embodimentsof the present invention without additional structural support.

A natural reaction of obstructed wind is to seek relief. The obstructedwind does so by diverting away from the obstruction. Thus the obstructedwind escapes around corners of the building adjacent to the buildingfacade that obstructs the wind, with a significant portion shifting toan upward vertical flow, seeking escape upwardly over the roof plane. Asobstructed wind moves vertically and combines, it speeds up, especiallyas it hits the escape point of the roof plane where it tends toaccelerate, while translating toward the horizontal. This is a“venturi-like” effect that causes increases in speed of up to about 20%.FIGS. 12A-12C are conceptual representations of such wind flow includingnatural horizontal wind flow W1 moving across the top of the skyscraperand natural horizontal wind W2 striking the facade 244 of the skyscraper242. As wind flow W2 strikes the building facade it forms acceleratedupward wind flow W3. Upward wind flow W3 in turn will be affected by theroof structure of the building as shown causing it to further speed upas it breaks into wind flow W4 and W5.

Embodiments of the invention capture such redirected and acceleratedwinds at the top of the building. For example, in turbine embodimentscontaining both vertically and horizontally disposed blades, thevertical wind components drive the horizontal (generally perpendicularto vertical axis) blades and the horizontal wind components drive thevertical (generally parallel to vertical axis) blades. Additionally, thehorizontal components of both building obstructed and unobstructednatural winds will be captured as they combine and move past thevertical blades of the turbine. This occurs at both the upwind anddownwind locations such that simultaneous driving of both the horizontaland the vertical blades can occur due to the turbine's naturalthree-dimensionality. Vertical components of wind are alsosimultaneously harvested by the horizontally positioned blades.

Natural, more traditionally flowing horizontal wind is also captured bythe embodiments containing both vertically and horizontally disposedblades. As the natural, generally horizontal wind first strikes theupwind vertically disposed blades, some of it will be slowed (resultingin force on the blade and torque on the device for power extraction.Much of it, however, will attempt to escape the obstructing blades andenter, go around and go over the turbine. The wind that penetrates theturbine or moves across the upwind blades flow across the inside of theturbine and will drive into the downwind blades during the turbine'srotation. This transfers additional power to those blades and producesadditional wind seeking relief. The escape route for the wind seekingrelief is between the downwind blades and redirection vertically. Theverticalized component is harvestable by the horizontal blades. Theseembodiments of the invention are therefore able to efficiently capturevertical components of the wind that are otherwise not harvested by thevertically disposed blades producing further torque via the horizontallydisposed blades that additionally transfers to the same generallyvertical axis.

The elements and structure of embodiments of the invention thatcapitalize on the described combination of natural (horizontal) andbuilding-induced updraft with both vertically disposed and horizontallydisposed blade configurations are mounted in one preferred embodiment ona suspended frame. The suspended frame design requires minimal structureto minimize the wind drag on the structure and thereby maximize theoverall efficiency of the device while still resisting the stresses ofturbulent and very high speed wind conditions. It comprises stiff topand bottom hoops and a system of struts and cables that together form alightweight structurally efficient framework that ensures that the hoopsoperate in tandem with minimal friction and inertial losses. In tyingtogether the upper and lower hoops, the framing elements and hoopscombine to create an efficient system that is inherently stable andstress resistant through its circular shape.

In preferred embodiments that employ both vertically and horizontallydisposed blades, the lightweight frame design allows the free flow ofboth generally horizontal natural winds as well as wind flow movingupwardly along the sides of a building and across its top. It alsofacilitates the vertical airflow diverted upwardly from the naturalhorizontal winds by the device itself as those winds strike the downwindvertical blades as the device rotates. In further embodiments of theinvention, where the turbine is sufficiently spaced from the tower topand the support and circulation zone under the device, the horizontallydisposed blades may be located both at the top and at the bottom of theopen frame within upper and lower hoops of the frame.

The frame structure that supports the blades preferably will begravity-supported on a hub mounted on a vertical mast. Magneticlevitation bearings or other types of bearings can be used to rotatablysupport the hub on the mast. In one preferred support arrangement, thehub concentrates the entire gravity weight of the fully assembled frameon the vertical mast. Thus, in this support arrangement of theinvention, when the turbine is mounted to a building roof, itefficiently transfers gravity loads and portions of the lateral loads ofthe turbine to the building through the mast. Other support arrangementsmay employ the entire primary vertical axis (mast) rather than the topmounted hub as a rotational element of the device. The hub in the firstsupport arrangement transfers some lateral loads into the mast, and thespinning lower hoop translates the remainder of any lateral loads intoits base. The spinning mast support arrangement transfers verticalgravity loads and lateral loads to the base through both the base of themast and the lower hoop. The first stationary mast support arrangementhas a lower hoop with lateral but no gravity/vertical component, and thesecond has lateral and gravity/vertical components.

Also, the frame design provides a generally balanced conditionespecially when spinning, with its rigid circular hoops resistinglaterally transferring stresses. In the first support arrangement, thelower hoop preferably will run along a fixed guideway that receives aportion of the horizontal lateral forces from the frame but avoidsgravity loading. The guideway may be fixed to the roof of a skyscraperor other building (or to a free-standing tower) so that it can gentlydisperse some horizontal lateral forces to the building across a largearea while stabilizing the entire assembly. The guideway may include awing-shaped deflector surface that streamlines some of the buildingupdrafts and directs them internally through the frame structure towardthe upper horizontal blades to assist in the capture of that windcomponent for beneficial harvesting of additional wind power by thedevice.

The lower hoop preferably will sit above the guideway so that it doesnot bear on the guideway, allowing all members supporting the lower hoopto be stressed into tension, enabling them to be generally smaller andthereby lighter than if gravity bearing and in compression. The guidewaypreferably also will be free of the hoop in the vertical direction by avariable dimension in order to accommodate temperature and other stressdeformations that can produce a variety of vertical displacementswithout causing added friction or vertical gravity bearing at thelocation of the lower hoop. In other words, since the lower hoop doesnot actually rest on the circular guideway, it is free to move upwardlyand downwardly in response to temperature and stress-related materialexpansion/contraction in the elements that make up the fully assembledframe structure as it rotates. In this way, the lower hoop and thereforethe vertical blades of the turbine are kept firmly in place with minimalfrictional losses. The structure acts like a “lamp shade” that issupported at the midpoint of its top. The hoops at top and bottom actlike the hoops in a hoopskirt to maintain its circular shape. The lowerguideway prevents “swaying” of the hoopskirt, but allows it to spinfreely. The “X” braced cable assembly ensures that the hoops rotate intandem but is nearly transparent (non-obstructing) to wind flow movinginto and through the turbine.

The frame structure with its vertical blades preferably will be amodestly truncated conical shape although it may also be cylindricallyshaped. It may also be an inverted truncated conical shape. The angle oftruncation may vary by 12° to the vertical in both directions. The openframe design produces an efficient transfer of all forces on theextremely lightweight frame structure to the vertical mast. The rotarymovement of the lower hoop is constrained by the circular guideway or inthe other embodiments via the tire-like supports that may driveelectricity generating units. The rotation of the top hoop is linked bythe open frame's triangulated structural tube to the lower hoop so thateach hoop moves in tandem with the other. The turbine frame is thusrestrained by the hub at the top of a vertical mast and furtherrestrained by the lower hoop and the circular guideway, but tiedtogether as one via the open system of rods and cables that make up thedevice's frame.

A key force that is also restrained and made less problematic inembodiments of the invention is the centrifugal force that results fromthe spin of the turbine. The primary components that receive the moststress are the vertical blades. These blades are stressed by the windforces and further stressed by the centrifugal forces of rotation. Anembodiment of the invention reduces the effect of these forces bybracing the rotatable vertical blades such that they tie into thecentral bracing structure in order to prevent outward deflection of theblade caused by these forces. The bracing ties the pivot rod of theblade, for example, at approximately the one third and two third heightpoints to reduce the unbraced length of the blade but still allowrotation. This further reduces the overall device weight and allows theblades to perform in an unhindered and efficient fashion.

As the device operates in the wind, the edges or faces of the spinninglower hoop may directly drive one or multiple conventional generatorpackages to produce electrical power on-site. Although it is currentlypreferred that the electricity will be generated using the edges orfaces of the lower hoop of the open frame to drive the generatorpackage, the turbine may be configured to engage other rotating surfacesor the rotating hub at the top of the vertical mast.

Rotatable vertical blades are mounted between the upper and lower hoops.The upper and in some embodiments, the lower hoop of the open frame ofembodiments of the present invention preferably will also carryhorizontally disposed blades that receive a portion of winds flowing upalong the sides of the building below and the redirected portions of thenatural horizontal wind that will also drive the turbine. A minimum ofthree horizontally disposed and three vertically disposed blades will beused. Currently, it is contemplated that about five horizontallydisposed blades and about five vertically disposed blades will be used.All of the blades should be rotatable about their long axes. Thevertical blades and also the horizontal blades may be controlled bymotor(s) or actuators or other mechanical devices powered by therotation of the device. Small generators driven by the main turbine canalso supply power to batteries for the actuators/motors that would driverotation of the blades per the direction of the TSR algorithm databasefor the turbine.

Horizontal wind capture will be maximized in embodiments of the presentinvention with vertical blades that are adapted to instantaneouslyadjust their position relative to the wind and speed direction as thedevice rotates about is vertical axis in order to maximize the torqueproduced.

Vertical wind captured will be maximized in embodiments of the inventionwith horizontal blades that are adapted to instantaneously adjust theirposition relative to the wind speed and direction as the device rotatesabout its vertical axis in order to maximize the torque produced. Asalready noted, in a preferred embodiment both horizontal and verticalwind capture will be achieved by vertical and horizontal blades,respectively.

The degree of rotation for each individual blade is different from eachof the others at any particular time and location about the radius ofthe turbine. Each instantaneous location may be determined by empiricaland mathematical algorithms to produce blade rotation and featheringthat maximizes the torque produced as the blades turn in the wind. Thecontrolling algorithm would optimize the torque at each blade for eachinstantaneously measured wind speed, turbine location, wind directionand other pertinent local variables.

A key element of the algorithms and the database produced for eachturbine location will be the careful monitoring of the tip speed ratioof the blades of the operating turbine so that torque production isoptimized. The controlling algorithm will also allow for other bladeangles that will achieve turbine start up in low winds and turbinebraking in high winds to prevent excessive rotation speeds that exceeddevice structural capacities and government safety regulations. Manualbrakes and locks may also be present to restrain rotation to accommodaterepair and maintenance schedules for the turbine.

The device controls vertical blade feathering angles at any rotationalangle through an algorithm that optimizes the torque of the device forany given wind speed and turbine rpm. The rpm is independently optimizedin order to achieve and maintain an optimal tip-speed ratio (TSR). Forvery high wind speeds, the TSR may be reduced in order to limit turbineRPM. For each operating point of the turbine as defined by its TSR,blade feathering angles are optimized to extract maximum torque from thewind striking and moving across the open frame. This controlinstantaneously optimizes power production, and can also be used tolimit rotational speed, as well as achieve auto-startup of the turbine.The blade feathering angle control also allows the turbine toinstantaneously adapt to the fluctuating wind velocities typical foratmospheric conditions encountered by the device. The control systemwill also be designed to prevent the device operating (excepttransiently) at any rotational speeds which might cause the dynamicforces to excite critical natural modes of vibration of the buildinginto resonance.

Blade Angle Control I

Blade Angle Control I is a preferred algorithm for achievinginstantaneous blade angle control of the vertical turbine blades. Due tothe circular motion of the blades relative to the oncoming wind, theblades experience an angle of attack of the air relative to the chordline of the blades “C” (shown in FIG. 10B) that varies periodically.Measuring the azimuthal position angle θ, counter-clockwise relative tothe backward-facing position of the blade arm, then the downwind angle β(measured in the same way as θ) of the air flow experienced by the bladewhen moving in the clockwise direction is given by

$\begin{matrix}{{{\beta(\theta)} = {{\beta(\theta)} = {- {\arctan\left\lbrack \frac{{{TSR}\cos}(\theta)}{1 + {{{TSR}\sin}(\theta)}} \right\rbrack}}}},} & (1)\end{matrix}$where TSR denotes the global tip-speed ratio which is the ratio of thespeed of the tips of the blades to the velocity of the wind wellupstream of the device.

$\begin{matrix}{{TSR} = {\frac{\omega\; R}{U_{\infty}}.}} & (2)\end{matrix}$

Here, ω is the angular speed of the wind turbine, R its radius, andU_(∞) the wind speed at a distance from the turbine where the flowvelocity is not significantly affected by the presence of the turbine.For example, the wind speed may be measured at a distance of about 1-2turbine diameters. Below, we will also make use of the concept of alocal tip-speed ratio T*, defined as

$\begin{matrix}{{{TSR}^{*} = \frac{\omega\; R}{U}},} & (3)\end{matrix}$where U is now the local free-stream velocity experienced by the bladeat its instantaneous location. This local velocity is different fromU_(∞) due to the fact that the operating turbine slows down the velocityof the wind in its vicinity. Calculations using the algorithm take intoaccount the fact that this reduction of wind speed will, in general, bedifferent at each angular position of the blade. In particular, aturbine blade will experience slower velocities for angles of−π/2<θ<π/2, corresponding to a blade position in the leeward-facing halfof the turbine, compared to the velocities experienced during thewindward half of its cycle.

FIG. 13A shows the angle-of-attack variation α₀(θ),

$\begin{matrix}{{{\alpha_{0}(\theta)} = {\frac{\pi}{2} + {\beta(\theta)} - \theta}},} & (4)\end{matrix}$that a blade mounted at a right angle to a radial turbine arm wouldexperience, as a function of the rotational angle θ relative to the winddirection. α₀ is defined positive if the relative velocity of theairflow experienced by the blade has a component pointing radiallyoutward, away from the rotational axis of the turbine.

In general, airfoils can only generate significant amounts of lift up toa certain maximum angle of attack, known as the “stall angle” α_(S).Above this angle, flow separation occurs, which is accompanied by abreak-down of lift, and a very significant increase in drag. Theairfoils that are used to generate lift forces have typical stall anglesα_(S)<15°, so with reference to FIG. 13A, at the tip-speed ratios we areaiming for (TSR<2.5), the fixed tangential blade experiences angles ofattack well in excess of the maximum angle of attack at which airfoilscan operate efficiently, which means that the airfoils of such a windturbine would operate in a stalled condition for a significant part oftheir cycle of revolution.

For regular (not stalled) flow conditions, the lift and drag forces arefunctions of the angle of attack of the air relative to the airfoil. Theexact dependency of lift and drag forces on angle of attack has to bedetermined experimentally or by numerical simulation, and depends bothon the airfoil shape and on the Reynolds number. These relationships areconventionally expressed in terms of the lift and drag coefficients,C_(L), and C_(D), respectively, defined via

$\begin{matrix}{{C_{L} = \frac{L}{\frac{\rho}{2}{SV}^{2}}},\mspace{14mu}{C_{D} = {\frac{D}{\frac{\rho}{2}{SV}^{2}}.}}} & (5)\end{matrix}$with L and D the lift and drag forces, respectively, p the density ofthe air, S the planform area of the blades, and V the velocity of theair relative to the moving blades. Taking the vector product of theforce vector F with the radius vector of the turbine arm, one cancalculate the torque T that each turbine blade generates. This torquewill thus be a function of the wind speed U_(∞), local tip-speed ratioTSR*, angle of attack of the blade a and of the rotational angle θ, sowe have T=T (U_(∞), TSR*, α, θ). It is important to note that, unlessthe angle of attack α is chosen judiciously, this torque will benegative (against the direction of rotation of the turbine), and that,for each set of the parameters given above, there is an optimal angle ofattack at each position of the blade during its rotation such that thepositive (driving) torque is maximized.

If the lift and drag coefficients C_(L)(α) and C_(D)(α) for givenoperating conditions of the turbine (wind speed and tip-speed ratio) areknown, an optimal angle of attack α can be determined by numericaloptimization. The optimal angle of attack for a given local tip-speedratio TSR* shows only weak dependence on the position of the blade ineach half-cycle of the turbine, which means that for optimal poweroutput, the turbine blades should be controlled in such a way that theyare at an almost constant absolute angle of attack relative to theoncoming flow velocity they experience. This angle of attack needs tochange sign at the ±90°-positions of the turbine arm in such a way thatthe resulting lift vector of the turbine blades has a component pointingtowards the rear, leeward side of the turbine. An example of theresulting blade angles of attack is shown in FIG. 13B. In order toachieve the angles of attack shown in FIG. 13B, the turbine blades needto be feathered at angles that vary throughout the rotation of theturbine. The feathering angles required to achieve the angles of attackgiven in FIG. 13B are shown in FIG. 13C. In FIG. 13C the featheringangle γ is defined positive for a rotation of the airfoil such that itsleading edge is pointing outwards, away from the axis of the turbine.

At lower tip-speed ratios (e. g. TSR<1.5) a greater variation on angleof attack is necessary to maximize the driving torque. It is clear thatthe achievement of optimal angles of attack would require abrupt motionsof the turbine blades at the ±90°-positions of the turbine arm that arenot practical, since they would require large forces, and enforcing themotions would consume significant power. In our design, these abruptchanges in angle of attack will be smoothed out. We note, however, thatthe torque provided by the blade of the turbine near these positionswill always be small (see FIG. 13D), so that the necessary deviationfrom the optimal angles of attack will only have a minor effect on thepower output of the turbine.

Adjustments of the blade feathering angles of the turbine may thus becarried out as follows:

-   -   The relationships for C_(L)(α, Re) and C_(D)(α, Re) for selected        blade sections are determined through single-blade tests in wind        tunnel experiments, or by numerical solution of the        Navier-Stokes equations governing the flow of air around the        airfoils.    -   Optimal theoretical feathering angles at each position (relative        to the incident wind direction) of each blade are determined for        the range of tip-speed ratios for which the device will operate.        The optimal practical feathering angles will be based upon the        theoretical values but adjusted to optimize the overall power        output (accounting for the local wind deceleration due to energy        extraction using, for example, the stream tube approximation,        and the energy that must be expended in feathering the blades)        and to minimize the effects of excessive feathering forces on        structural and mechanical design. In order to do so, the power        output of the turbine over a full revolution is determined as a        function of a set of practical feathering angles. This set of        angles is optimized to maximize the net power output.    -   In one embodiment of our turbine, each of the blades will be        equipped with velocity sensors that can determine instantaneous        airspeed and velocity for each blade, a short distance ahead of        the blade. This can be done using, for example, hot-wire or        pitot probes 164 mounted on stakes 162 protruding ahead of the        blade as shown, for example, in FIGS. 1A and 10.    -   Another embodiment of our turbine may use sets of at least two        pressure sensors 166 mounted on the front and back of the        turbine blades themselves, as shown, for example, in FIG. 11. By        combining information from several pressure sensors mounted on        both sides of the airfoil, it is possible to determine both        angle of attack and velocity of the airflow experienced by a        turbine blade. By using information from sensors of a preceding        blade, the wind conditions that will be encountered by the        following blade can be predicted, simplifying the design, and        improving the performance of an appropriate control algorithm.    -   A control algorithm will be implemented which, based on        instantaneous readings of the above sensors, determines optimal        feathering angles in order to follow a smoothed relationship        analogous to the one given in FIG. 3.    -   The controller sends appropriate signals to actuators on each        turbine blade that adjust the feathering angles accordingly.

Blade Angle Control II

In an alternative embodiment, optimal feathering angles as representedfor a particular example in FIG. 13C can be approximated by a sinusoidalfunction. This means feathering angles follow a relationship of the formγ(θ)=γ₀ cos(θ+Φ₀),  (6)where γ₀ is the feathering amplitude, and Φ₀ is a phase shift. For thisembodiment, the parameters γ₀ and Φ₀ are determined by directlyoptimizing the power output of a turbine using the feathering anglesgiven by equation (6). In order to do so, the power output of theturbine over a full revolution is determined as a function of γ₀ and Φ₀using, for example, the stream tube approximation. Values for γ₀ and Φ₀are then determined such that this power output is maximized. Ingeneral, these optimal values will depend on wind speed and tip-speedratio. The advantage of this approach is that one need only to determineone representative wind speed and direction for the turbine, which canbe measured by a single sensor, in addition to the turbine speed inorder to determine tip-speed ratio. Control of the blade featheringangles can then be carried out through mechanical means or with anelectrically powered actuator.

For this embodiment, the blade feathering angles of the turbine areadjusted as follows:

-   -   The relationships for C_(L)(α, Re) and C_(D)(α, Re) for selected        blade sections are determined through single-blade tests in wind        tunnel experiments, or by numerical solution of the        Navier-Stokes equations governing the flow of air around the        airfoils.    -   Based on the data from either experiments or simulation, the        power output of a turbine using the feathering angles given by        equation (6) is determined.    -   By numerical optimization, we determine values for γ₀ and Φ₀ are        determined such that this power output is maximized. The optimal        parameters will depend on wind speed and tip-speed ratio.    -   In one embodiment, the turbine will be equipped with velocity        sensors that determine instantaneous direction and speed of the        wind. A pitot probe is suitable for this purpose, but other        sensors capable of determining direction and magnitude of the        wind speed may be used.    -   A control algorithm will be implemented which, based on the        instantaneous readings of the above sensors, determines optimal        parameters for amplitude and phase of our eccentric control        device.    -   The controller sends appropriate signals to actuators that        control the parameters γ₀ and Φ₀ angle of the blades.

Feathering techniques either similar to those described above or otherfeathering techniques already available in the art may be used in thepractice of this invention.

Measurements

Instantaneous air flow measurements may be obtained by locating hot-wireor pitot probes 164 on stakes 162 with the tip of the tube about oneblade cord length ahead of each blade, as illustrated in FIG. 1A. Theinstantaneous flow velocity vectors from the measured flow velocitiesand flow directions can be determined using known conventionaltechniques from the data produced by the hot-wire or pitot probes oneach blade. Using this data, the blade angles can be controlled as setforth below for each blade for the instant that the blade reaches thelocation of the tube tip based on the instantaneous flow velocityvectors to determine and implement optimal feathering angles of theblade.

Alternatively, pressure sensors 166 such as piezo-electric pressuresensors, pitot static sensors, LIDAR or SODAR sensors 166, can bemounted on the front and the back of each of the blades. This isillustrated in FIG. 11. There must be at least one sensor on each sideof each blade, but preferably there it will be two or more sensors oneach side. From these pressures the instantaneous flow velocity vectorcan be determined using conventional techniques. This flow velocityvector can be used to predict the feathering necessary for thenext-following blade.

The above instantaneous flow determination techniques are illustrated inFIG. 16.

The Blade Angle Control I technique described above is illustrated inFIG. 17.

TABLE I Look-Up TSR γ₀ Φ₀ • • • • • • • • • • • •

The Blade Angle Control II technique described above is illustrated inFIG. 18. The implementation of this technique requires the placement ofa plurality of wind direction and speed detectors spaced from theturbine.

TABLE II Look-Up For each selected TSR: θ α θ₁ • θ₂ • θ₃ • θ₄ •

FIG. 13 diagrammatically illustrates one set of feathering angles forvertical blades 140A-140E at a TSR of 1.5. Thus, in this figure there isa horizontal wind blowing in direction Dl. Blade 140A is feathered at216 degrees with respect to the wind direction, blade 140B is featheredat 288 degrees, blade 140C is feathered at 0 degrees, blade 140D isfeathered at 72 degrees and blade 140E is feathered at 144 degrees.

FIG. 14A diagrammatically illustrates feathering angle variations whenTSR is altered. Thus, FIG. 15A shows the position of blade 140A atTSR=1.5. FIG. 15C shows the position of the blade at TSR=2.0. FIG. 15Cshows the position of the blade at TSR=2.5. Finally, FIG. 15D shows theposition of the blade at TSR=3.0.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to aid in understanding the invention, it will now be describedin connection with exemplary embodiments thereof with reference to theaccompanying drawings in which like numerical designations will be givento like features with reference to the accompanying drawings wherein:

FIG. 1 is an axonometric view of one embodiment of the invention;

FIG. 1A is axonometric view of another embodiment of the invention;

FIG. 1B is a partial sectional view of the lower roller supportconfiguration of the embodiment of FIG. 1A;

FIG. 1C is a perspective view of the bicycle wheel and spoke supportingstructure of the upper and lower hoops of the embodiment of FIG. 1A;

FIG. 1D is a perspective view of the central bearing structure of FIG.1B;

FIG. 1E is an elevation view of the apparatus shown in FIGS. 1A-1D;

FIG. 1F is a partial sectional view of the lower area of the rotatablemast and associated supports, bearings and cabling of the embodiment ofFIG. 1A;

FIG. 1G is an axonometric view of another embodiment of the invention inwhich horizontally disposed blades are located at the top and bottom ofthe open frame structure;

FIG. 2 is a top plan view of the embodiment of FIG. 1;

FIG. 3 is an axonometric view of the guide rail and vertical mast of theembodiment of FIGS. 1 and 2;

FIG. 3A is an axonometric view of the mast support cabling of theembodiment of FIG. 1;

FIG. 3B is a partial cutaway elevation view of the hub of the devicemounted at the top of the mast of the embodiment of FIG. 1;

FIG. 3C is top plan view of the hub assembly of the embodiment of FIG.1;

FIG. 3D is a partial cut-away view showing the mounting of the proximalpivot rods of the embodiment of the FIG. 1;

FIG. 4 is an axonometric view showing the bicycle rim and spokesconfiguration of the upper hoop of the embodiment of FIG. 1;

FIG. 5 is an axonometric view of the lower hoop juxtaposed above theguideway of the embodiment of FIG. 1;

FIG. 5A is a partial cross sectional view showing the relationship ofthe guideway, the lower hoop, and the generator package of theembodiment of FIG. 1;

FIG. 5B illustrates a braking mechanism of the embodiment of FIG. 1;

FIG. 5C is a partial view of primary and secondary wind flow deflectorsmounted to the support rods of the piers holding the guideway of theembodiment of FIG. 1 in place;

FIG. 6 is an axonometric view of the lower hoop of the embodiment ofFIG. 1 showing anchor points for support rods;

FIG. 7 is axonometric view corresponding to FIG. 6 in which X bracinghas been added to help triangulate forces on the support rods and lowerhoop;

FIG. 8 corresponds to FIG. 4 but includes X bracing to help triangulateforces acting on the upper hoop;

FIG. 9 is an elevation view of the fully assembled central supportstructure of the embodiment of FIG. 1 of the invention;

FIG. 10 is a partial axonometric view of the embodiment of FIG. 1showing the generally vertically disposed blades juxtaposed above theirattachment points on the lower hoop;

FIG. 10A illustrates various features of the system for counteringcentrifugal forces on the vertical blades as used in both embodiments ofthe invention;

FIG. 10B is a partial cross sectional view of the centrifugal forceresisting features of the FIG. 10A;

FIG. 11 is an elevation view of the embodiment of FIG. 1;

FIGS. 12A-12C are conceptual drawings showing wind flow adjacent a tallbuilding and against and within a wind turbine in accordance withembodiments of the present invention;

FIG. 13A is a graph of the angle of attack variation that a blademounted at a right angle to a radial turbine arm would experience;

FIG. 13B is a graph of an optimal angle of attack for a given tip-speedratio;

FIG. 13C is a graph of the feathering angles required to achieve theangles of attack shown in FIG. 13B;

FIG. 13D is a graph of the torque provided by a turbine blade near thechanges in the blade angle of attack at the plus or minus 90 degreepositions of the turbine arm;

FIG. 14 shows vertical blade angles as the frame of the turbine rotatesat a fixed TSR;

FIGS. 15A-15D are representations of blade feathering angles at a setturbine rotational angle and varying TSR values;

FIG. 16 is a flow chart illustrating instantaneous flow determinationtechniques;

FIG. 17 is a flow chart illustrating the Blade Angle Control Itechnique; and

FIG. 18 is a flow chart illustrating the Blade Angle Control IItechnique.

DETAILED DESCRIPTION OF THE INVENTION

Turning first to FIGS. 1 and 2, an open frame structure 10 is shown hungfrom a vertical mast 20 that will be described in more detail below. Theframe structure includes a circular lower hoop 80 and a circular upperhoop 110. Lower hoop 80 is positioned above a guideway 60 (FIG. 4) thatis supported by a series of piers 62 disposed about the circumference ofthe guideway.

Although five vertical blades 140A-140E are shown evenly spaced aboutthe circumference of the frame structure supported on the lower hoop, ascurrently preferred, a minimum of three such blades may be used. Also,although five optional horizontal blades 170A-170E are shown radiallydisposed within upper hoop 110, as currently preferred, a minimum ofthree such blades may be used. Additionally, although five optionalhorizontal blades 171A-171E are shown radially disposed within lowerhoop 60 in FIG. 1G, as explained earlier, such lower horizontal bladesare not required but if used, a minimum of three such lower horizontalblades may be used. Also, the structure may be provided with horizontalblades only adjacent the top of the open frame structure, only adjacentthe bottom of the open frame structure or disposed at both the top andthe bottom of the open frame structure. Finally, although the framestructure is indicated to rotate in a counterclockwise direction “D”, itcan be arranged to rotate in a clockwise direction as well. The internalarea of the frame encompassed by the vertical blades is the centralpassage 12 of the frame.

Turning now to FIG. 3, vertical mast 20 is shown fixed and mounted in amast base 22. The mast may include ladder rungs 31 to provide access tothe top of the mast for maintenance and repair purposes. The mastpreferably will be braced by appropriate mast support cabling runningfrom near the top of the mast. As seen in FIG. 3A, such mast supportcabling 21 is attached at its distal end about the mast at locations 23and 25 and extends at its proximal end to cable attachment eyelets 24 oneach of the piers. Of course, if desired, the proximal ends of thecables can be attached to other appropriate non-rotatable structures.This mast support cabling helps vertically brace the mast allowing itsunbraced length to be reduced and its structural requirements lessened.As a result, the weight of the entire structure is reduced.

While the mast base may be of any appropriate design, in the illustratedembodiment it includes a flat bottom plate 26 supporting a centralmember 28 into which the mast is fixed and mounted. Bottom plate 26 alsoincludes holes 30 to receive fasteners (not shown) for attaching base 22to a roof deck, a tower, or to other supporting surfaces or structures.

Mast 20 carries the gravity load of the turbine and frame 10 of theillustrated embodiment of the invention to receive and resist portionsof the lateral forces experienced by the frame. The mast may be of anyappropriate length. It also may taper upwardly from the base of themast. For example, in one embodiment the mast may be about 80 feet tallto accommodate a frame having a height of about 60 feet leaving aclearance spacing of about 20 feet under the bottom of the frame. Theclearance spacing should have sufficient vertical height to provide agap to admit air flow moving across the wall-two-roof transition point(or “edge” of the roof) to the center of the open frame of the turbine.

A rotating hub assembly 32 is mounted at the top of vertical mast 20 asshown in FIGS. 3-3B. As best seen in the cross-sectional view of FIG. 3Band the plan view of FIG. 3C, the hub assembly includes a cylindricalhub housing 33 dimensioned to fit over the top portion 34 of mast 20.One or more rare earth magnets 35 are mounted in the top 36 of housing33. One or more like magnets 37 rest in a cavity 38 at the top of themast. Magnets 35 and 37 are positioned with like polarities oppositeeach other so that they repel producing a low friction MAGLEV bearingeffect. Other bearing types may of course be used. Additionally, housing33 is kept centered on the top of the mast by bearing packs 39 that areattached to the inner wall 40 of hub housing 33 so that they ride alongthe outer surface 41 of the top portion 34 of the mast, transferringlateral forces from the upper hoop to the mast.

FIG. 3B also illustrates one of the five actuator enclosures 42 whichare each dedicated to a different vertical blade distributed evenlyabout the outside of hub housing top 36. Each of these enclosuressupports a proximal pivot rod 172 of one of horizontal blades 170A-170Ein a bore 174 fitted with bearings 176. Opposed actuator driver arms 178and 180, which engage the outer surface of rods at diametrically opposedlocations, will shift up and down in response to thealgorithm-controlled operation of actuators (not shown) to rotate therods in order to feather the angles of the blades to maximize the poweroutput of the turbine. It should be noted that alternatively matinggearing or direct drive arrangements may be provided about the rod andalong the driver arms. Indeed, various different known types ofactuators can be used, including an electro-hydraulic actuator.

Additionally, a small generator 43 may be located in the actuatorenclosure. Generator 43 includes a rotary member 44 that engages theouter surface 41 of the top portion 34 of the mast as it rotates,driving the generator. This generator maintains a charge in batteries 45that power the actuators.

A series of upper attachment brackets 46 project radially from the top36 of the hub housing and a like number of lower attachment brackets 47project radially from an area adjacent the bottom of the hub assembly.Brackets 46 and 47 include eyelets 48 for receiving upper hoop cabling50.

Turning now to FIG. 4, upper hoop 110 is shown affixed to hub assembly32. The upper hoop includes inwardly directed top and bottom lips 52 and54 that have eyelets 56 for receiving upper hoop cabling 50. Upper hoopcabling 50 is thus run between the eyelets in top and bottom lips 52 and54 and the eyelets 48 in upper and lower attachment brackets 46 and 47of hub 32 to fix the upper hoop to the hub in a “bicycle wheel-and-hub”configuration.

As seen in FIG. 5, vertical mast 20, which is centered within the areacircumscribed by a guideway 60, establishes the center point of the plancircle of the turbine and the center point of the guideway over whichlower hoop 60 is positioned. Piers 62, which support the guideway,include a base 68 and a rod 69 running vertically upward which isattached to the guideway. Piers 62 rest on and are in turn affixed to ahigh rise building roof deck or other supporting surface or structure(not shown).

FIG. 5A is a cross-sectional view which best illustrates the generallyinverted “T” shape of the guideway with the base of the inverted “T”labeled 64 and the longer leg of the “T” pointing vertically upward sothat it forms an annular flanges that is received in a correspondingannular cavity 82 of lower hoop 80 of the device. This relationship maybe reversed with the cavity in the guideway to receive an annular flangeon the hoop.

Posts 66 also support one or more generator packages 70 that may be ofconventional construction and will be employed as explained in furtherdetail below. For example, the generators may be of a permanent magnettype, having suitable cut-in speeds of about 15-200 rpm. Conventionalpower electronics may be used to convert the alternating currentproduced by the generators to an appropriate voltage and frequency usinga conventional rectifier, d.c. stage adjustment and inverter.

Lower hoop 80 is shown in FIG. 5 juxtaposed above guideway 60. FIG. 5Ain turn shows a partial view of the guideway in its final positionwithin the lower hoop. Lower hoop 80 thus includes an annular downwardlydirected cavity 82 that receives bearing assemblies 84 mounted onopposite sides of center leg 61 of the guideway. The bearing assemblies84 are positioned and dimensioned to engage the inner walls 88 of cavity82. This ensures that lateral movement of the lower hoop is smooth withlow friction but constrained by the guideway which braces the lower hoopto oppose lateral forces and yaw while keeping the circular rotation ofopen frame structure 10 true.

Also, since in this embodiment the lower hoop sits above rather than onthe guideway it is guided by but not gravity supported on the guideway.Since the vertical blades as well as many components of the framestructure will expand and contract with outdoor temperature changes andin response to other stresses on the system, this lower hoop/guidewayarrangement will accommodate such expansion and contraction “E/C” (FIG.5A) while ensuring proper rotation of the frame structure. In lesspreferred embodiments of the invention, however, the lower hoop may reston the guideway or an alternative hoop restrainer structure.

Turning to FIG. 6, lower hoop 80 is shown including a series of evenlyspaced anchor points 90 along the inner wall 91 of the hoop forattachment of support rods 95, as will be described below. Lower hoop 80also includes a series of upstanding pins 93 (or alternatively cavities)that receive the gravity load of vertical blades 140A-140E transferredby the pivot rods of the blades, as also will be described below.

Lower hoop 80 is positioned above the guideway for travel incounterclockwise direction “D”. Lower hoop 80 is hung from hub assembly32 in a “maypole-like” configuration by a series of support rods 95 thatare affixed at their proximal end to the bottom hoop as shown in FIG. 5Aand at their distal end to the hub as shown in FIG. 3B. As can be seenin FIG. 6, the support rods are preferably attached opposite the bearingpoint of each vertical blade to minimize potential interference with theblades as they pivot.

Support rods 95 are interconnected by a central support cable 96 whichencircles and is attached to the support rods preferably near theirmidpoints 98. Central support cable helps the entire interconnectedsystem of support rods 95 and the cabling associated with the upper andlower hoops to withstand centrifugal or outwardly directed forcesexperienced during rotation of the frame structure of the turbine. Thecentral support (as well the various other cables) described herein)cable preferably will be fitted with turnbuckles (not shown) to permitit to be tensioned when the frame structure is assembled and to permitfuture adjustments as required to meet design standards for the device.It is preferred that the central support cable lie in a generallyhorizontal plane forming a middle pentagonal hoop in the illustratedconfiguration, to minimize interference with movement of blades140A-140E and wind currents that flow across or within the framestructure.

Lower “X” braces 100 in FIG. 7 are formed with cabling running from thepoints of attachment of central support cable 96 to the two support rods95 to anchor points 90 on the lower hoop. The “X” braces may be affixedat their crossover points 101. The lower “X” braces help to efficientlytriangulate the forces acting on the support rods and the lower hoop toassist in conjunction with the upper “X” braces attached to the upperhoop, to allow the lower hoop to more synchronously and therefore intandem with the upper hoop and the central hub.

FIG. 8 depicts upper “X” braces 104 comprising cabling running from thebottom of top hoop 110 to the rod midpoints 98. The upper “X” bracescomplete the “tube” began the lower the lower “X” braces.

FIG. 9 shows the fully assembled frame of the turbine, with the bladesremoved. This is the central bracing structure 106 of frame 10. Thecabling and rod supports described in connection with FIGS. 6-8 andshown as well in FIG. 9 not only ensure that the upper and lower hoopsmove synchronously, i.e., in tandem, they also make the open framestructure extremely lightweight. This minimizes drag due to friction,and achieves a substantial reduction in impediments to movement ofnaturally occurring and generally horizontal wind across the frame whilealso allowing vertical building induced wind to move vertically throughto the horizontally disposed blades. The five lower “X” braces, whichefficiently triangulate forces and reduce the mass of the overallstructure, form a tube (structurally) in conjunction with the five upper“X” braces. Each are connected to a hoop and acts as a system that tiesthe tubes together for synchronous movement. The tube links through thecenter hoop at the plane of central support cable 96 which acts like abelt, reducing its expansion through the action of centrifugal forces.

FIGS. 1A-1F illustrate an alternative embodiment of the invention inwhich a rotating vertical mast 20A with a magnet bearing includingopposed magnets 35A and 37A is used to support an open frame 10A. Inthis embodiment upper hoop 110A is mounted to the top of the mast with abicycle wheel hub-and-spokes arrangement 130 generally as described inconnection with the earlier figures and as illustrated in FIG. 1C. Lowerhoop 80A is similarly attached to vertical mast 20A with a bicycle wheelhub-and-spokes arrangement 132. However, since the bottom hoop is now aframe supporting member (there is no structure corresponding to guideway60), a series of rollers 83 are evenly spaced about a bottom annularsurface 81 of hoop 80A. In the illustrated embodiment, bottom annularsurface 81 is angled about 45 degrees to the vertical and rollers 83 aresupported on piers 85 at a corresponding angle (FIG. 1B). This helpsmaintain the frame 10A in alignment as it rotates. Finally, one or moregenerator packages 70A may be driven by rollers 83.

The remaining features of the frame of this alternative embodiment aregenerally as described above in connection with the embodiment of frame10, and more particularly as shown in FIGS. 1D and 1E.

FIG. 10 illustrates the positioning of vertical wind energy harvestingblades 140A-140E on upstanding pins 93 of lower hoop 80, although asnoted above, cavities for receiving the blade pivot rods may be usedinstead of pins. Upper hoop 110 has been removed in this figure forpurposes of better viewing.

Although vertical blades 140A-140E (as well as horizontal blades170A-170E and 171A-171E) are symmetrical in shape with chord C bisectingthe blades, irregularly shaped blades with a curved central core may beused. Also, although blades 140A-140E are referred to as “vertical” or“generally vertical” we mean by these terms that these blades may betilted±12° from the vertical (i.e., both inwardly and outwardly from thevertical), with upper and lower hoop diameters adjusted as necessary,forming truncated conical shapes, a cylinder (at 0°) and invertedconical shapes. Currently, it is preferred that the vertical blades beat an angle of +6°, with a smaller hoop at the top, as shown.

Each of blades 140A-140E has an outer surface 142 and an inner surface144 as well as a leading edge 146 and a trailing edge 148 and a top edge154 and bottom edge 156. The blades may be hollow or filled and may bemade of aluminum, carbon fiber, or other appropriate materials. Theblades will be affixed to a pivot rod 151 centered between the inner andouter surfaces of the blade that establishes a longitudinal pivot axis150. Also, when tip speed ratio (or TSR) is referred to herein the “tip”is an imaginary point 102 (FIG. 10) on the pivot axis 150 (or theaverage radius R taken along the pivot axis from the top hoop to thebottom hoop).

The vertical blades are subject to variable centrifugal force tending todeflect or bend the blades causing bowing and other deformations thatwould interfere with blade efficiency as the turbine frame spins. Theamount of deflection or bending of the blades is dependent upon thecentrifugal force exerted and the length of the blade. Typically, for agiven force, the degree of deflection can be reduced by making thestructure of the vertical blades more robust and therefore heavier or bymaking the blades shorter, thereby limiting the output of the turbine.

The present invention, however, provides a unique alternative approachto controlling deflection of the vertical blades. This is illustrated inFIG. 10A in which a bearing ring 182 is shown comprising a rigid outerring 188 with a series of ball bearings 190 rotatably fixed on its innerdiameter. The bearing ring is attached to a bearing cable 192. In theillustrated embodiment, bearing rings 182 are located at approximatelyone-third and two-third positions on pivot rod 151 preferably withbearings 190 riding in a slot 194 in the rod. The rings (and bearingcables) may, of course, be attached at other intermediate locationsalong the pivot rod. An opening 196 is formed opposite the bearing ringsso that cable 192 can extend from the rod to attachment points 94 onsupport rods 95. Opening 196 must be wide enough to prevent interferencebetween cable 192 and the inner surface 144 of the blade as it pivotsabout the pivot rod. These cables and their attachment to the pivot rodallow rotation of the blade to occur with limited friction while greatlylimiting deflection or bending of the blades.

FIG. 10B illustrates the centrifugal forces. Thus, in this figurevertical blade 140A is shown with one feathering position in solid linesand another feathering position in broken lines. As the frame rotatesthe blade will experience centrifugal forces in direction CF. Theseforces are opposed in direction OF by cable 198 which is attachedpreferably at a 90° angle to ring 182.

FIG. 11 shows the wind turbine with both upper hoop 110 and lower hoop80 in place and the vertical blades mounted therebetween. This figurehighlights how the frame structure of the present invention is able topresent the vertical blades on the periphery of the frame structure withno outer members that would interfere with wind capture and an internalstructure offset from the periphery to avoid physical interference withthe vertical blades that rely upon thin cables and support rods forsupport and therefore because of their small effective diameter alsopresents minimal interference with wind flow moving across or within thestructure.

Returning now to FIG. 2, horizontal blades 170A-170E are shown extendingbetween the inner surface 200 of upper hoop 110 and the outer surface ofhub assembly 32. The horizontal blades include proximal and distal pivotrod 202 and 204, respectively, that define the axis of rotation of theblades. Proximal pivot rods 202 is rotatably mounted in the outer wallof actuator enclosure 42 as shown in FIG. 3B and discussed above. Distalpivot rod 204 projects inwardly from enclosure 205 which is formed onthe inner surface 200 of the upper hoop. Enclosure 205 includes a bore203 through which the distal pivot rod extends with bearings 206encircling the bore and a bearing ring 208 which together ensure trueand relatively friction free rotation of the horizontal blades as theyare pivoted to maximize operation of the turbine. Also, as can be seenin FIG. 3C, enclosure 202 has a clearance area 210 beyond the distal endof pivot rod 204 so that the rod may move back and forth radially toaccommodate expansion and contraction of the horizontal bladecomponents.

In one embodiment of the invention, the horizontal and vertical bladesmay have controlled blade movements that are coordinated to maximizewind capture based on the varying wind speed of the induced and naturalvertical winds as measured at the locations of the blades. Thehorizontal and vertical blades may also move independently. Also, itshould be noted that while the axes of the horizontal and verticalblades may be in any relationship from aligned to evenly offset at themidpoints between the blades, it is currently preferred that the bladesbe evenly offset as shown in the figures. This, it has been found,produces a significant improvement in power output of the turbine.

It is currently preferred that the rotating wind turbine will drive oneor more generators 220 as depicted in FIG. 5A. As shown in this Figure,generator 220 is fitted with a generally horizontally disposed tire 222mounted on generator shaft 224. The tire is positioned opposite theinner wall 91 of bottom hoop 80. The generator is mounted in aspring-loaded sled 228 to maintain frictional contact between the outersurface of the tire and the inner surface of the hoop. Thus, as thelower hoop rotates, it will cause tire 222 to rotate, driving thegenerator and producing electrical current. The natural gearing ratio ofthe lower hoop diameter and the tire diameter are beneficial to therotational speed of the generator rotor. The spring will also be“releasable” for tire changes and other repairs.

FIG. 5B shows a braking mechanism 230 which is mounted on guideway 60.The braking mechanism includes a laterally disposed brake piston 232that extends and retracts brake pads 234. Thus, when it is desired tostop the device and lock the lower hoop (for repairs and maintenance,for example), the piston is activated extending the brake pads untilthey frictionally engage the inner walls 88 of annular downwardlydirected cavity 82 of the lower hoop. Preferably a plurality of brakeswill be evenly disposed about the circumference of the guideway. Thesebrakes may also be used to finish the job of the blade featheringcontrol algorithms by reducing the speed of rotation where necessary toachieve an appropriate TSR.

FIG. 12A is a conceptual representation of components of such a tallbuilding (or tower) induced air flow that are believed to be importantto embodiments of the invention that include both generally verticallyand generally horizontally disposed blades. Thus, horizontal arrows W1represent the natural horizontal wind moving across the roof of thebuilding and arrows W2 represent the natural horizontal wind strikingthe façade 244 of the building. Arrows W1 and W2 increase in length fromground level 236 to the level of the parapet 240 of roof 236 of tallbuilding 242 to reflect the increasing wind speeds as the distance fromthe ground increases.

Preferably, primary deflectors 252 are attached to support rods 69 ofpiers 62.

In FIG. 12B, mast base 24 is shown affixed to the top of the elevatorcap housing 246 of a building 242. Frame 10 preferably is dimensionedand positioned so that it extends to at least one edge 250A of the roof,preferably at least two edges (i.e., at a corner of the roof or acrossthe shorter dimension of a rectangular roof), more preferably at leastthree edges, and most preferably four edges (i.e., where the roof issquare). This will maximize capture of building-induced wind flow.Preferably the angle and height of the primary deflectors will be chosenand adjusted, i.e., “tuned” to the characteristics of the specificbuilding to best deflect a portion of the building induced winds W3 intocentral passage 12 of the open frame, as explained below. In theillustrated embodiment, the primary deflectors are at an angle of about85 degrees to the roof surface. In a preferred embodiment, secondarydeflectors 254 also will be mounted on support rods 69. The secondarydeflectors will be refined in shape and angle for each installation asthe combination of upper and lower deflectors are dependent on thebuilding's shape, form and surface texture for their optimal“spoiler-like” action in directing a portion of the wind flow into theturbine for optimum harvesting by the blades.

FIG. 5C shows primary and secondary deflectors 252 and 254. Althoughprimary deflector is flat and secondary deflector has a curved outersurface 255 in the illustrated embodiment, as noted above, the shape,size and positioning of the deflectors will depend upon installationsite parameters. It is intended however that the building-induced windflow will be deflected into gap G between the deflectors and intocentral passage 12.

In FIG. 12B the open frame structure 10 is shown mounted with its bottom256 at a height relative to roof 238 and primary deflectors 252 whichwill optimize the movement of a portion of the vertical wind flowthrough the bottom of the open frame structure and into central passage12 and into the horizontal blades as shown in FIG. 12C.

Thus, as wind flow W2 strikes the building outer surfaces in FIG. 12C itforms an accelerated upward wind flow W3 (as well as diverginghorizontal flow toward each edge of the building). Upward wind flow W3in turn will be affected by the roof structure of the building as showncausing it to further speed up as it breaks into a firstbuilding-induced wind current W4 and a second building-induced wind flowW5.

As shown in this figure, wind flow W4 will flow up through centralpassage 12 to strike and help drive the horizontal blades and wind flowW5 will strike and help drive the vertical blades. Finally, the backsurfaces of the rotating vertical blades of the open frame structurefacing into central passage 12 will force generally horizontal wind flowmoving past the vertical blades into a flow W6 moving primarily upwardlyto further help drive the horizontal blades.

Thus, horizontal wind flow W1 (FIG. 12A) which strikes vertical blades140A-140E will cause the open frame structure to rotate. A portion ofwind flow W1, however, will move past the outer surfaces of the bladesand across the center of the open frame structure striking the backs ofthe opposite blades and be deflected back into the central passage and aportion will escape the leeward side 14 of the turbine. Since verylittle of this deflected wind will be able to escape through the bottomof the frame, it will generally be deflected upwardly to help drive thehorizontal blades.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention are to be construed to cover boththe singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of any and all examples, orexemplary language (e.g., “such as”) provided herein, is intended merelyto better illuminate the invention and does not pose a limitation on thescope of the invention unless otherwise claimed.

Finally, preferred embodiments of this invention are described herein,including the best mode currently known to the inventors for carryingout the invention. It should be understood that the illustratedembodiments are exemplary only, and should not be taken as limiting thescope of the invention.

The invention claimed is:
 1. A method for harvesting energy from windflow, the method comprising: receiving, at a controller for a windturbine, measurements corresponding to wind flow for a first blade of aplurality of blades of the wind turbine, wherein each of the pluralityof blades is a generally vertically disposed blade that is i) rotatableabout a respective vertical blade axis, and ii) mounted near a peripheryof an open frame structure of the wind turbine that is rotatable about acentral vertical axis; determining, by the controller, localized airflowcharacteristics for the first blade based on the measurements;determining, by the controller, a feathering angle for a second blade ofthe plurality of blades based on the local airflow characteristics ofthe first blade; causing, by the controller, the second blade to rotateabout the respective vertical axis based on the determined featheringangle.
 2. The method of claim 1, wherein: determining the localizedairflow characteristics for the first blade comprises determining thelocalized airflow characteristics for the first blade when the firstblade is near a first azimuthal position about the central verticalaxis; causing the second blade to rotate comprises causing the secondblade to rotate about the respective vertical axis based on thedetermined feathering angle when the second blade is near the firstazimuthal position about the central vertical axis, wherein the firstblade is adjacent to and precedes the second blade during rotation aboutthe central vertical axis.
 3. The method of claim 1, wherein the localairflow characteristics include an angle of attack of the wind flowrelative to the first blade and a local airflow velocity of the windflow.
 4. The method of claim 1, wherein receiving the measurementscomprises receiving air pressure measurements from air pressure sensorslocated on first and second opposing sides of the first blade.
 5. Themethod of claim 4, wherein the air pressure sensors include a firstplurality of sensors located on the first side of the first blade and asecond plurality of sensors located on the second side of the firstblade.
 6. The method of claim 5, wherein each of the plurality of bladesincludes respective first and second opposing sides, a respective firstplurality of sensors located on the corresponding first side, and arespective second plurality of sensors located on the correspondingsecond side.
 7. The method of claim 4, wherein determining the localizedairflow characteristics comprises determining instantaneous flowvelocity vectors based on a plurality of wind flow velocities.
 8. Themethod of claim 1, wherein determining the feathering angle comprises:determining lift coefficients and drag coefficients for an airfoil shapeof the plurality of blades; generating a table of feathering angles forthe plurality of blades according to azimuthal positions about thecentral vertical axis and localized tip speed ratios of the plurality ofblades based on the lift coefficients and drag coefficients for theairfoil shape.
 9. A wind turbine for harvesting energy from wind flow,comprising: an open frame structure that is rotatable about a centralvertical axis; a plurality of blades, wherein each of the plurality ofblades is a generally vertically disposed blade that is i) rotatableabout a respective vertical blade axis, and ii) mounted near a peripheryof the open frame structure; a plurality of actuators, wherein each ofthe plurality of actuators is configured to rotate a corresponding bladeof the plurality of blades to a selected feathering angle; a pluralityof sensors coupled to the plurality of blades; a controller that causesthe actuators to rotate the plurality of blades to respective featheringangles based on a respective azimuthal position of the correspondingblade about the central vertical axis; wherein the controller receivesmeasurements corresponding to wind flow for a first blade of theplurality of blades, determines localized airflow characteristics forthe first blade based on the measurements, and determines the featheringangle for a second blade of the plurality of blades based on the localairflow characteristics of the first blade.
 10. The wind turbine ofclaim 9, wherein the controller: determines the localized airflowcharacteristics for the first blade when the first blade is near a firstazimuthal position about the central vertical axis; and causes thesecond blade to rotate about the respective vertical axis based on thedetermined feathering angle when the second blade is near the firstazimuthal position about the central vertical axis, wherein the firstblade is adjacent to and precedes the second blade during rotation aboutthe central vertical axis.
 11. The wind turbine of claim 9, wherein thelocal airflow characteristics include an angle of attack of the windflow relative to the first blade and a local airflow velocity of thewind flow.
 12. The wind turbine of claim 9, wherein the plurality ofsensors include air pressure sensors located on respective first andsecond opposing sides of the plurality of blades.
 13. The wind turbineof claim 12, wherein the air pressure sensors include a first pluralityof sensors located on the first side of the first blade and a secondplurality of sensors located on the second side of the first blade. 14.The wind turbine of claim 13, wherein each of the plurality of bladesincludes respective first and second opposing sides, a respective firstplurality of sensors located on the corresponding first side, and arespective second plurality of sensors located on the correspondingsecond side.
 15. The wind turbine of claim 12, wherein the controllerdetermines instantaneous flow velocity vectors based on a plurality ofwind flow velocities.
 16. The wind turbine of claim 9, wherein theplurality of sensors include one or more of piezo-electric sensors,pitot-static sensors, lidar sensors, or sodar sensors.
 17. The windturbine of claim 9, wherein the plurality of sensors include one or morehot-wire probes or pitot probes mounted ahead of respective leadingedges of the plurality of blades.
 18. The wind turbine of claim 9,wherein at least some of the one or more hot-wire probes or pitot probesare mounted one blade cord length ahead of a corresponding blade of theplurality of blades.